1. Field of the Invention
The present invention relates to a rubber composition. More particularly, it relates to a rubber composition for a tire tread.
2. Description of the Related Art
Passengers cars now have very high performance due to, for example, the enhanced power output of engines and the lightening of body weight. As a result, starting, accelerating and turning properties of the car are significantly improved.
The improvement in such moving properties requires high steering stability and a tire which transmits the power of the car to the road surface. Also, the recent environmental protection and energy-efficiency requirements require reduction in the rolling resistance of the tire (low heat build-up) and high wear resistance.
In order to ensure steering stability, it is necessary to enhance grip force at the tread part which shows high energy loss properties, for which various improvements have been made.
Examples of conventional methods for enhancing the grip force of a rubber in a tread material include a method wherein a large amount of high reinforcing carbon black is formulated in a rubber composition for tire treads, and hardness and modulus are controlled by a plasticizer. However, internal heat build-up becomes high, and the stiffness of the tread is also deteriorated due to rolling resistance or changes hardness in the driving. While further, when an excessive amount of the plasticizer is added, wear resistance is extremely deteriorated.
There is also a method of enhancing the molecular weight of a rubber in a tread material to improve heat build-up and wear resistance. However, workability becomes inferior, and enhancement of the molecular weight has its limits.
As described above, grip force, heat build-up and wear resistance of the tire tread material are antinomic to each other, even if a conventional material is used. Therefore it has been considered to be impossible to improve both of the above properties, simultaneously.